LAKE STATES ASPEN REPORT NO. 9

ASPEN LUMBER FOR BUILDING PURPOSES

BY LOUIS W. REES MINNESOTA AGRICULTURAL EXPERIMENT STATION UNIVERSITY OF MINNESOTA

DECEMBER 1947

PROCESSED BY U.S. DEPARTMENT OF AGRICULTURE FOREST SERVICE LAKE STATES FOREST EXPERIMENT STATION FOREWORD

During and since World War II, there has been increasing interest in aspen (Populus tremuloides) in the Lake States, its availability and supply, properties and uses, and management. Aspen is a tree of primary importance in 20 million acres or 40 percent of the total forest area of the three Lake States - Michigan, Minnesota, and Wisconsin.

At an informal meeting ~t Madison, Wisconsin, in January, 1947, forestry representatives of several federal, state, and industrial groups in the Lake States agreed that it would be desirable to bring up-to-date what is known on aspen and make it available to anyone interested. The job of preparing this ·information in the form of reports was assigned to each of the groups listed below. The reports will be duplicated as rapidly as completed, and the entire project should be finished by the end of 1947. Each report will concern one aspect of the subject, Copies will be available from the Lake States Forest Experiment Station or from each contributor.

Report Number Subject

1 Aspen Properties and Uses 2 Aspen Availability and Supply 3 Logging Methods and Peeling of Aspen 4 Milling of Aspen into Lumber 5 Seasoning of Aspen 6 Aspen Lumber Grades and Characteristics 7 Mechanical Properties of Aspen 8 Machining and Related Properties of Aspen 9 Aspen Lumber for Building Purposes 10 Aspen for Containers 11 Aspen for Core Stock 12 Small Dimension and Other Industrial Uses of Aspen 13 Aspen for Veneer 14 Aspen for Pulp and Paper 15 Aspen for Cabin Logs 16 Aspen for Excelsior 17 Aspen Defiberization and Refining of Product 18 Chemical Utilization of Aspen 19 Preservative Treatment cf Aspen 20 Marketing of Aspen 21 Possibilities of Managing Aspen 22 Enemies of Aspen

Contributors of Lake States Aspen Reports

Lake States Forest Experiment Station, St. Paul 1, Minn. Forest Products Laboratory, Madison 5, Wis. North Central Region, U, S. Forest Service, Milwaukee 3, Wis. Div. of Forestry, Univ. of Minnesota, University Farm, St, Paul 1, Minn. School of Forestry and Conservation, University of Michigan, Ann Arbor, Mich, Department of Forestry, Michig~n State College, East Lansing, Mich, Michigan College of Mining and Technology, Houghton, Mich. Superior Wood Products, Inc,, Duluth 2, Minn. Forestry Agent, Chicago~ North Western Railway System, St. Paul 1, Minn, ZM 92942 F REPORT NO. 9

ASPEN" LUMBER FOR BUILDING PURPOSES

By

Louis W. Rees, Associate Forester Minnesota Agricultural Experiment Station University of MinnesotP

INTRODUCTION

Recent shortages of lumber for building purposes make it desirable to seek out all possible supplies of additional lumbe~~ Aspen, according to a study made in northern Minnesota during 1944,1' may be a source of lumber largely untapped. The results of that study are the ma.in basis of this paper.

In the past, aspen has received little consideration as a source of lumber, largely because of the small-sized trees often harvested and some prejudice against the wood. However, because it is abundant and has many favorable characteristics, aspen can be used much more widely for lumber.

Quaking aspen, Populus tremuloides Michx., has the widest range of any North .American tree species. Bigtooth, Populus grandidentata Michx .. , while less abundant, often grows with quaking aspen. The wood of both species is marketed as aspen or "popple." Although the aspens grow on a wide variety of soil and site conditions, it is only on the best sites that they reach sawlog size.

The main stands of aspen are located in the Lake States, the north­ eastern United States, and in the central Rocky Mountain region. In the Lake States, there are 20 million acres of aspen type with a total saw-timber stand of nearly 6} billion board feet. Of this amount, about one,,.half is located in Minnesota.. Full utilization of the aspen stands for all the products they can produoe can gree.tly in.prove the general prosperity of the Lake States forest area.

CHARACTERISTICS OF ASPEN LUMBER THAT AFFECT ITS USE FOR CONSTRUCTION PURPOSES Physical Propertie~

The fresh wood of aspen is normally white in color. On exposure it becomes grey or a pale grey-brown. The wood at the center of the tree is often discolored, and this discolored wood is often mistaken for

1/ Conducted by the writer as a cooperative study between the Minnesota Agricultural Experiment Station and the Lake States Forest Experiment Station. 3./ See Lake States Aspen Report No. 1 for a more detailed discussion. heartwood. Knots are numerous, comparatively small, generally tight, and often surrounaed by discolored wood which makes the knot appear larger than it actually is. While knots decrease the strength of wood, these defects along with various discolorations are not objectionable for certain uses in building construction. However, wood containing decay should not be used.

Aspen lumber is easily air seasoned or kiln dried, but there is some loss from collapse in kiln drying. The collapse occurs primarily in the areas of discolored or brown-stained'wood. Lumber up to 2 inches thick, properly piled and air seasoned, is satisfactory for most build­ ing purposes. Lumber that is piled during the winter or early spring should be ready for use in building construction in late summer and early fall of the same year. Since the lumber is often subject to warping and twisting during the drying process, the importance of good piling practice cannot be overemphasized. Perhaps some of the other properties of aspen wood can best be brought out by comparison with a well-kn.own structural wood such as eastern white pine. At 12 per cant moisture content, aspen is slightly heavier than eastern white pine. It has more shrinkage than eastern white pine, but less than that of many other woods used for similar purposes. With improper seasoning, as for most other woods, shrinkage may be consider­ able (see figure 1).

Figure 1.--Tha white streaks show the amount of shrinkage in green aspen bevel siding after one year of service. It is also evident that the overlap was not sufficient. The founda­ tion is too low to protect the lower courses of boards from ground :moisture. Photo by Forest Products Laboratory. Mechanical Propertie~ Aspen wood has lower nail-holding pmver than that of eastern white pine. Soft woods, such as eastern white pine and aspen do not split readily during nailing and more or larger nails can be used. This will tend to overcome, a.t lea.st in part, low nail-holding ability. However, the size of the nail should not be increased to the point ,where it will ca.use the wood to split. In one locality in northern Minnesota. it was believed that the nail,,.;holding power of aspen was greater than that of eastern white pine or red pine. Consequently, in constructing gothi.c sawed rafters, aspen wood was used at the center while the red pine boards were -nailed to eith~r side. The position of the two woods should have been reversed. The loss in nail-holding power when green aspen is used and allowed to sea.son in place is greater than that for most woods and may be as much as 90 per cent. Loss in nail-holding power and the amount of shrinkage which occurs during seasoning a.re both good arguments for the proper seasoning of the material before use.

In static bending, a. property iinporta.nt in beams, joist, and rafters, aspen is a.bout equal to ea.stern white pine. Its stif.f':ness and compres­ sion parallel to the grain are somewhat less, while its shock resistance or toughness is greater than that of ea.stern white pine. All of these properties a.re important in structural woods.

Durability and Pa.int-holding Qualities of Aspen Wood

Aspen wood is not durable. It cannot be expected to last more than three or four yea.rs, and may decay considerably in one year, when used in places where the moisture content of the wood will remain compara­ tively high. The danger points in buildings are: (1) sills, (2) joists and subfloc,rs in buildings without a. basement and where the ventilation is poor, (3) interiors of poorly ventilated barns and other fa.rm build­ ings, (4) steps' and porch columns, and (5) posts resting on the ground or on concrete or embedded in concrete. Aspen wood used in such places should be treated with a wood preservative in order to prolong its ser­ vice life.

Aspen wood, a.long with basswood and cottonwood, stands at the top of the list of hardwoods in paint-holding ability. This is one reason why aspen wood has been used for interior finish, especially in places where it is to be painted. The wood also takes a. good natural finish and such figure as the wood possesses shows up fairly well. Ordinary house pa.int, when applied to aspen wood for exterior use, should last four yea.rs before repainting becom_es riecessa.ry (See figure 2). Good quality iron­ oxide pa.int will la.st a.bout six to seven years.

Y See Lake States Aspen Report No. 7 for a more detailed discussion.

-3"· panel drop siding panel after covering one-half of Figure 2.--Aspen all knots three coats of white lead paint. Note that with paint surface covered well. After two years' service, the was still in excellent condition.

Planing Properties of Aspen about woods, planes best at a :moisture content of Aspen, like most other siding on the over-dry weight of the wood. The drop 6 per cent based content of in figure 2, hmvever, was surfaced at a moist.ure panel shown a good surface 15 per cant, and it was smooth enough to present about in the photograph, for painting. In some of the pieces, not evident of furring. Another defect which TIJB.Y develop there was a slight amount and fur­ during planing is chipped grain. Chipped grain in aspen lumber of knota. occur in the irregular grain in the vicinity ring generally purpoaea if the defects can be overcome aufficiently for building Theae knives are kept aharp lumber ia thoroughly air seasoned and the planer and placed at the correct angle. Sizes of Aspen Lumber Produced

The ma.in objection to the use of aspen lumber for building purposes is that the boards a.re narrow, variable in width, and generally short. Most aspen logs have been cut in 100-inch lengths. At most mills, how­ ever, aspen lumber of greater length can easily be produced when such is desired.

A study ma.de at a. box facto~y mill located in northern Minnesota. showed the number of boards and the a.mount of lumber produced from 2,940 (100 inch) aspen logs ranging in diameter from 5 inches to 15 inches at the small end. Although boards from 3 to 14 inches in width were produced, the greater pa.rt of them were between 4 and 7 inches (table 1).

Table 1.--The amount of a.s en lumber roduced in boards of various widths from 2!940 100-inch aspen lo€js Per cent of Width of boards Number of Lumber sea.le I boards I total Inches Board feet

3 1,558 3,195 4.8 4 2,558 6,807 10.3 5 3,706 12,264 18.5 6 3,059 12,425 18.8 7 2,144 10, 150 15.3 8 1,516 9,296 140 1 9 905 5,619 8.5 10 478 3,266 4.9 11 218 1,662 2.5 12 119· 1,006 1.5 13 51 455 .7 14 3 28 • 1

Total 66,173 100.0

About one-third of the total lumber sea.le was produced in boards 5 inches or less in width. The remaining two,,thirds of the total scale was in boards 6 inches or over in width. Although they have their limitations, narrow boards can be used for building purposes. Boards 4 inches wide are often made into flooring while boards 6 or 8 inches wide can be ma.de into shiplap, drop siding, or bevel siding. Care in sawing and increas­ ing the size of the smallest log would largely eliminate material less than 4 inches in width. It would be desirable to cut only lumber from logs- which are at lea.st 8 inches in diameter a.t the small end.

Quality or Grade of Aspen Lumber Produced

Aspen lumber for building purposes usually is not graded. To obtain information on the approximate grade distribution of aspen lumber, the boards listed in table 1 were g"ra.ded according to hardwood grading rules

-5- for construction lumber. About 4.5 percent of the total lumber scale graded as A and B finish. About 13 percent of the total scale graded as Noo 1 construction boards; 32 percent as No. 2 construction boards; and 45 percent as No. 3 construction boards. The remaining 5.5 percent con­ tained considerable decay and were considered as unfit for building pur­ poses. At another mill, also located in northern Minnesota, aspen logs were cut mostly into 8/4 inch dimension stock. The dimension stock ob­ tained from 321 aspen logs graded approximately 33.5 percent No. 1 dimen­ sion and 61.5 percent No. 2 dimension. The remaining 5 percent were dis­ carded because of the presence of decay. Ninety-five pe'rcent of the logs from which this stock was produced were between 5 inches and 9 inches in diameter at the small end. A.11 the logs were 100 inches long. The material was cut in widths of 4, 6, and 8 inches. PRESENT USE OF ASPEN LUMBER FOR CONSTRUCTION

In 1945, about 15,000,000 board feet of aspen lumber were used in the Lake States for building construction--most of it in rural areas. Such use has developed almost entirely during the past decade.

Most of the aspen lumber used for building construction is cut locally, often from the mmer' s woodland. Generally it is seasoned and then hauled to a local planing mill for further processing where that is feasible. It is often found in lumber yards in the northern part of Minnesota, especially in those which are operated in conjunction with a combined sawmill and planing mill. Most of this material is in the form of flooring, shiplap, or dimension. However, at least one Minne­ sota mill will manufacture aspen into any desired building product.

Aspen lumber is rarely handled by independe~t lumber yards outside of the commercial range of the species, One of the main reasons is that the boards are relatively narrow and short, which increases the cost of handling~ especially in building construction. Another objection is that the price is generally too high to compete with the lower grades of pine which are widely used for building purposes. Apparently there would be considerable demand for the higher grades if these could be obtained in sufficient quantities.

During the survey made in northern Minnesota in 1944 about 25 buildings were examined in which at least some aspen had been used. Thirteen of these buildings were dairy barns. However, aspen lumber was also being used in construction of other farm buildings such as chicken houses, granaries, ma.chine sheds and garages. It was also used in residence construction in both rural and urban areas. Severa]. cases were also noted where aspen logs were used ip the construction of log houses and cabins.

Usually aspen lumber is not selected for any particular use. Commonly it is mixed with other structural woods growing in the region and used for all building purposes, provided the pieces are large enough to fit the requirement. It has been used satisfactorily for sills, girders,

-6- girder posts, joist, studding, ra.f'ters, sheathing and roof boards, sub­ floors, flooring of various types, interior finish and o.f'ten in the form of drop siding or bevel siding for exterior finish. In some cases, it is also used for shingles. A dairy barn, located near Bagley, Minnesota, built in 1944, was constructed entirely of aspen, even to the shingles • .Another dairy barn (see figure 3) which was built in 1942 near Waubon, Minnesota, used the following material (ahdost all local wood)i

l. Sill - northern bur oak 2. Girder posts - aspen 3. Girders - aspen and northern bur oak 4. Girder caps - northern bur oak 5. Joist - aspen and some northern bur oak 6. Mow floor - aspen - 6-inch flooring 7. Studding - aspen 8. Plate - northern bur oak 9. Rafters - (bent type) aspen 10. Sheathing and roof boards - aspen 11. Exterior finish - basswood bevel siding 12. Shingles - western red cedar 13. Window frames - aspen 14. Stanchions, stalls, and mangers - aspen

It is not intended that this list should indicate the wood best suited for a given purpose. It is merely an outline of the different woods used in construction of this particular barn. However, the barn is well con­ structed. The fotmdation is about 8 inches above the floor on the inside The girder posts are set on a cement base projecting about 6 inches above the cement floor level. A durable wood was used for the sill and the inside of the barn is well ventilated. Many other cases could be cited with minor variations from the outline given ~bove.

Figure 3.--Dairy barn constructed in 1942 using about 90 percent aspen lumber. -7- RECOMMENDATIONS FOR THE UTILIZATION OF ASPEN LUMBER FOR BUILDING CONSTRUCTION

Aspen lumber has been used for the construction of an entire building. However, the inherent qualities of the wood make it more suitable for some uses than for others. An understanding of these qualities and how to use or treat the wood will aid in. obtaining more satisfactory results.

Since aspen wood is not durable, it should not be used without preserva­ tive treatment in places where it is subject to decay. In most build­ ings the sill is most subject to decay. The sill is also one of the most vital spots in building construction, Either a durable wood, such as the heartwood of white oak, northern bur oak, or northern white cedar, should be chosen, or else the nondurable wood should be given careful treatment with a good wood preservative.

Aspen lu1nber is best suited for sheathing, roof boards, and subflooring. No. 3 construction boards can be used for these purposes. The lumber can be used in the rough, to decrease building costs, surfaced on one or both sides and one or both edges, or in the form of shiplap. Surfac­ ing at least on one side and on one edge is desirable as it makes a smoother surface for the application of the exterior layers and allows boards of uniform width to be placed in a given sheathing course. Ship­ lap makes a tighter form of construction and can be made in different widths. If they are cut about 7/8 inch in thickness, boards to be used in the rough will approach the standard thickness of yard lumber after it has been air seasoned. It is important that lumber used in the rough should be accurately sawed as to thickness and width. Inaccuracy in savring is one of the commonest objections to the use of rough home-savm lumber for building construction.

Since aspen wood is not strong and often contains defects, it must be used with a certain amount of caution for framing materials such as studdin , joists, and rafters. For small buildings such as chicken 6 1 houses, garages, granaries, and small houses.1 aspen 2 x 4 s are strong enough for studding and in many cases for rafters, especil:).lly where the rafter is short. In large buildings such as dairy barns, the studding should be made of 2 x 6 1 s and the joist, not over 12 feet long, of 2 x 8 1 s or larger. The joists in the barn shown in figure 3 are most­ ly aspen 2 x 8 1 s. However, a few joists of the same size are made of northern bur oak.

There are a number of ways of increasing the strength of joists. A joist which is full 2 x 10 in size is 36 ,Per cent stronger than one surfaced to standard size of 1 5/8 x 9. 1/2. Doubling the width or doubling the number of joists would double the strength, while to in­ crease the depth from 8 inches to 10 inches would increase the amount of wood by 25 per cent, a.nd increase the strength about 56 per cent. Ca.refully sawed joists can be used in the rough, For ease in construc­ tion, however, it is better to have the joists surfaced on the edges in order that they ma.y be uniform in depth.

-8- ln many instances, aspen 2 x 6's have proved satisfactory for rafters in ~ambrel roof 0 barns where the longest rafter was not over 14 feet. . Most dairy barns are built with the gothic roof, using either sawed or bent- type nailed rafters. Either type made of aspen has proved satisfactory where sufficient laminations of material have been incorporated into the rafter. Six layers of 1 x 4 aspen boards appear to be about the minimum for the construction of substantial bent nailed rafter. Such a rafter placed 2 feet on center was used in constructing the barn shown in f'igure 3. One case is kno'W7). where gothic rafters were constructed with 4· layers of 1 x 4 aspen boards. Every fourth rafter was well braced on the inside. That such bracing was insufficient and, further, that the rafters were not well designed are indicated by the fact that the un­ braced rafters have settled considerably, giving the roof a sway~-back effect.

Because of its painting qualities, aspen lumber has been used for some time as interior finish. In some cases it has been used for interior paneling and finished in natural color. It is often used in the form of shiplap or at least finished on one surface for interior finish of barns, garages, and other farm buildings. A garage near Greaney, Minne­ sota, was lined with aspen shiplap in 1929. It was still in good condi­ tion in 1944 after 15 years of service. A dairy barn near Aitkin, Minnesota, built in 1942, is similarly lined.

Aspen wood is often used for exterior finish. It is sometin.es used in the rough for this purpose. Rough aspen lumber used on the exterior of a warehouse located near Greaney, Minnesota, was in good condition in 1944 after 19 years of service. Similar material used on the lower part of a barn located near Fertile, Minnesota, was also in good condi tion after 22 years of service. In both cases the saw marks are still present on ths surface of the boards. There are numerous cases where aspen drop siding has been used. It is.also made into bevel siding. Vfuen aspen lumber is made into siding, it is probably best to make some selection of the better material, such as No • . 2 construction boards or better. Most defects in this lumber will cover well with paint (see figure 2).

It is important that good construction practice be followed in applying any siding. .Bevel siding is lap,ped 3/4 inch for 3-inch siding, l inch for 6-inch siding, and 1 1/2 inch for siding over 6 inches. This lap is sufficiently great so that a nail will go through the bottom portion of one piece and through the top of the piece beneath. Failure to pro vide enough overle.p is illustrated in figure 1, where mo13t of the nails missed the top edge of .the boards entirely.

That aspen lumber can be used for flooring has been amply demonstrated. The mow floor in the barn shown in figure 3 was made of 6· 0 inch aspen flooring. A planing mill at Bagley, Minnesota, was floored with 2·,.inch rough aspen planks • .An aspen store floor in a northern Minnesota tovm. was laid in 1908 and was still in use after 34 years of service. Prop- erly seasoned aspen flooring appears to wear smoothly. --

-9- Very little is known regarding the use of aspen shingles. A small barn built near Swatara, Minnesota, in 1938, was covered with aspen shingles. The roof was still in good condition in 1944, Another barn, built in 1944, was covered with aspen shingles. The owner, basing his statement at on previous experience, said that he expected these shingles to last a least 15 years. It should be possible to treat aspen shingles with wood preservative which would probably double their service life. On roofs with considerable pitch, untreated aspen shingles may perform reasonably well, but they should never be used on low pitch roofs unless first treated with a wood preservative.

SUMMARY has been Aspen lumber can be used successfully for building purposes 9 as illustrated by several eY..amples, if the inherent qualities of the wood are used to best advantage and good construction practices are followed. be To SUJJllnarize the previous discussion and to emphasize precautions to observed in good building practice, the following points should be fol­ lowed: (1) Build on a well,0 ,drained site; (2) use lumber that has been thoroughly air seasoned for framing, sheathing, etc., and kiln-dried lumber for interior finish of homes; (3) use a naturally durable heart­ be wood or treat aspen lumber with a good wood preservative if it is to ex used for sill.s or in other places where it is subject to decay; (4) tend foundation walls at least one foot above the ground to keep the in wood awe.y from ground moisture; ( 5) provide for adequate ventilation barns and beneath floors where there is no basement., (6) see that insula­ ana. tion materials are properly 'used; (7) make tight construction joints use drip caps over doors and Ydndows,. BIBLIOGRAPHY

(1) Bell, L. E. and Jefferson, C, H. 1944. Use of Jack Pine and Popple for Farm Buildings. Mich. State College Ext. Bul. 255, 23 pp., illus. (2) Betts, II. S. 1944. American Woods--Aspen. Forest Service, U. S. Dept. Agr., Washington, D. C. (3) Browne, F. L. 1942. Painting Hardwoods in Farm Buildings. Forest Products Laboratory Mimeo. 1291, U. S. Dept. Agr. (4) Christopherson, Cc H. and Rees, L, W. 1945. Home Grown Timber for Fa.rm Buildings. Minn. Fa.rm and Home Science, Vol. II, No. 2, illus. (5) Cunningham, R, n. 1946. Revised Forest Statistics for the Lake States. Lake States Forest Experirnent Station Paper No. 1, illus. (6) Forest Products Laboratory 19i8. Nail Holding Power of American Woods. Forest Products Laboratory Tech. Note No. 236, U, S. Dept. Agr, (7) Forest Products Laboratory 1940. Methods of Applying Wood Preservatives. Forest Products Laboratory Mimeo. Rl54, U. S. Dept. Agr. (8) Johnson, R. P.A., Kittredge, J., and Schmitz, H, 1930. Aspen--Availa.bility, Properties, and Utilization. Univ. of Min..~. Agr. Expt. Sta. Tech. Bul. No. 70, 72 pp., illus. (9) National Hardwood Lumber Association 1944. Rules for the Measurement and Inspection of Hardwood Lumber, Cypress, Veneers and Thin Lumber, Nat. Hardwood Lbr. Asso. Chicago (10) Schwantes, A. J., and White, H.B. 1945. Fa.rm Building Priorities for the Postwar Period. Minn. Farm and Home Science, Vol. III, No. 1 (11) Sweet, C. V., and Johnson, R, P. A. ·. 1936. Selection of Lumber for Fann and Home Building. U. S. Dept. Agr. li'nrmers Bul. No. 1756. 45 pp., illus. (12) White, C.H. 1942. Home Grown Timber for Fa.rm Buildings. Univ. of Minn. Agr. Ext. Bul. 238, 16 pp., illus.

(13) Zasada, Zigmond, and Kluender, ·v{. A. 1946. The Future of Aspen in the Lake States. Chemurgic Digest, Vol. V, No. 11.

-11-